Various types of spinal column disorders are known and include scoliosis (abnormal curvature of the spine), kyphosis (backward curvature of the spine), spondylolisthesis (forward displacement of a lumbar vertebra), and other disorders such as ruptured or slipped discs, broken or fractured vertebrae, and the like. Patients who suffer from such conditions usually experience extreme and debilitating pain. In severe cases treatments for these conditions have used a technique known as fusion with spinal fixation which results in the surgical/mechanical immobilization of areas of the spine and the eventual fusion of the vertebrae in the regions treated. In less severe cases treatment comprises decompression of the affected nerve and fusion of the vertebrae involved.
Spinal fixation procedures use the implantation of screws into the vertebra in the affected region of the spine. Clamps are attached to the screws. The clamps are, in turn, clamped onto a rod which spans adjacent vertebra and thus fixes the vertebrae relative to each adjacent vertebrae. Since there is a large individual variation in the curvature of the spine and relative positioning of anchor screws in the vertebrae, the rods have to be bent to correctly "meet up" with the clamps.
Bending of the rod adjusts for differences: in the location of the clamps once they are positioned on the screws; in left-to-right displacements; and in the elevation of the clamp, which is often angled, relative to the plane of the spine (the anchor screws are often placed at different angles in the vertebrae to ensure they are placed in the safest part of the vertebrae). As a result of these differences rod receiving apertures of the clamps do not align. Therefore, the rod must be bent so that it can align with the rod receiving apertures of the clamps even apart from bending needed to induce normal spine curvature.
Bending of the rods is normally performed once the screws and clamps are in place in the vertebrae. Therefore, this must take place during the surgical procedure, while the patient remains under anesthetic. The bending of the rods, therefore, prolongs and, as a result, may adversely affect the outcome of the surgery. Also, bending the rods requires great skill on the part of the surgeon and requires extensive manipulations of the rods. These manipulations may lead to an increase in the possibility of contaminating the rod and, thereby, increasing post-surgical infection. Also, bending of the rods introduces the possibility of developing stress fractures in the rods and, because the rods are bent during surgery, the structural integrity of the bent rods can not be checked.
Adjustable screws and clamps have been used in an attempt to eliminate the amount of rod adjustment required to properly clamp the rods in place. One such device incorporates an articulated clamp allowing rotation of the rod relative to the plane of the spine. Another device, described in U.S. Pat. No. 5,053,034 to Olerud, uses a "spinal joint" which allows rotation of the rod relative to the plane of the spine. These devices do not allow the clamps to be elevated relative to the plane of the spine nor do they allow for right-to-left adjustments. Also, the adjustable elements introduce the possibility of the clamps loosening during use.
Another device is described in U.S. Pat. No. 5,002,542 to Frigg and a device of a similar function is described in U.S. Pat. No. 5,129,900 to Asher et al. These devices allow adjustment in the distance of the rod from the screw, i.e. right-to-left adjustment by use of a slot adjustment. However, these devices do not allow for adjustment of the height or angle of the clamps. Again the adjustable elements of these designs introduces the possibility of the elements loosening after implantation.
Another adjustable design is described in U.S. Pat. No. 5,030,220 to Howland and uses a spacer to adjust the height of the clamp above the plane of the spine. However, this design does not allow for right-to-left adjustment or adjustment of the angle of the clamp. Also, the use of a spacer requires the assembly of a number of small components during surgery. This can be difficult under surgical conditions with gloved hands.
It is desirable that a fixation device be provided which facilitates connection of the rod to the clamps. It is further desirable that such a device does not require manipulation of multiple small components. It is also desirable that such a device has only a few moveable parts, which could loosen after implantation.